1. Field of the Invention
This invention relates to detection of explosives or narcotics, and more particularly to dislodging and removing particles of substances from a surface in order to facilitate the transport, capture, detection, and identification of the particles.
2. Description of Related Art
There exist a wide variety of instruments that are capable of detecting and identifying target particles of narcotics and explosives once the sample of particles is transported to the instrument and subsequently vaporized. Examples include, but are not limited to, ion mobility spectrometers, mass spectrometers, gas chromatographs, surface acoustic wave sensors, cantilever beam sensors, and electron capture detectors. Similarly, there are several ways that may be utilized to transport the target particles to the instrument, some of which are incorporated within the instrument and some which may require an operator to perform the transfer. Examples include, but are not limited to, mechanically transporting a collected sample to the instrument, vacuum collection of vapor or particles, and vortex vacuum sampling.
The target particles begin by being attached to a surface by weak chemical bonds, van der Waals forces, mechanical attachment in a fibrous structure or porosity, adhesive forces, electrostatic attraction, or entrainment in a sticky material, such as grease. For narcotics and explosives target particles, the surface adhesion forces can be relatively strong, making the target particles difficult to remove by simple, low momentum transfer methods, such as blowing a puff of air. Removal of such strongly adhered target particles by blowing air is usually successful only for the largest, heaviest target particles that present the greatest surface area to the blowing air. In general, blowing air does not readily remove target particles of explosives or narcotics from rigid surfaces, only from flexible surfaces, such as cloth, where the fluttering motion of the material provides the momentum to mechanically dislodge the target particles. Even with cloth, the blowing air stream usually requires a very high velocity flow to have any effect and then only for the largest target particles, so the process is very inefficient.
In some cases, the process of taking a sample begins with an operator or a machine physically wiping an absorbent, often textured substance, such as chemical filter paper, onto the surface to be tested. Target particles of the chemical of interest may then be transferred and concentrated on, or in the surface texture of, the absorber by the mechanical action of the wiping. This intermediate absorber is then brought to the vicinity of the detection instrument to make a measurement. The wiping method generally works reliably and efficiently but can be costly, because the media usually has to be replaced often, and a trained operator is often required.
There are many applications in which it may be desirable to avoid having to manually wipe a surface. These include, for example, sampling without an operator, large area sampling, remote sampling, robotic sampling, and situations in which the frequent replacement of wiping materials is not acceptable. In these cases a better method of dislodging target particles from the surface than simply blowing air may be desirable.